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The company building a rotating detonation engine is pushing the tech forward (arstechnica.com)
65 points by CharlesW 9 months ago | hide | past | favorite | 44 comments



All of these hypersonics companies are targeting mach 5 for a reason, which is that the material science hasnt caught up yet. The bet seems to be that they'll either be ready once it is, or they'll be the ones to develop it and start raking in a mountain of military industrial complex cheese.

Not a bad goal, but the thin vernier of 'passenger flight' leaves a bad taste in my mouth. This tech is for munitions delivery first, the meatbag ferry is squarely a side hustle, and I wish they'd be honest about it.


I'm in the industry... It's a constant psychological game. The type of highly educated people necessary to pull off these ventures are less interested in being part of the MIC than they used to be. Nationalism in that crowd is thankfully much less aggressive than it was during the cold war. As such, founders have resorted to lying about their goals so they can expand their applicant pool for developing the tech, then "pivot" and get acquired by Raytheon et al.

I also think to some extent there are employees who know but semi-appreciate the cover. In a prior life, I worked on some stuff that's, unfortunately, currently being used to murder people in the middle east. That just doesn't make good small talk at parties.


I'd hope some of these employees are looking at what is happening to Ukraine and reconsidering their positions. Without weapons of your own, you're beholden to unfriendly nations with their own weapons.

Certainly I get the sense that a lot of Ukrainians have reconsidered their own views. There's people I know who I doubt would have ever involved themselves in weapons development, who have gotten into it and related things.


What's used in Ukraine today may be killing Gazans tomorrow. I'm not an absolutist, I'm still in the industry, but I have rules on what I'll build for people.


It might be, or it might not be. Weapons can be used for good or bad, just like most things.

Also, some weapons are less useful for bad purposes than others: a missile-defense or air-defense system, for instance, isn't terribly useful for bombing civilian populations, and it's kinda hard to criticize someone for wanting to shoot down incoming missiles. Dumb bombs, on the other hand, are great for bombing ground targets, which could be either Russian invaders or cities with trapped civilians.

However, if you're a SWE as many people here probably are, and you get into the business of building weapons for war, a lot of the stuff you'd work on probably isn't that useful for killing Gazans. To kill lots of Gazans, you just need things like dumb bombs, artillery shells, etc. Those things don't use software; they've been using those weapons since WWI or before. The "smart" weapons the expensive SWEs work on aren't so useful for indiscriminate killing of civilian populations: they're much more accurate, but also much more expensive, so if your goal is just to kill civilians, they're not a very good way to spend your money. It's much easier to just get lots of artillery shells and shoot them in the general direction, just like Russian troops do.

Engineers in many different industries can be blamed for enabling awful things. Facebook engineers, for instance, I think have a lot to answer for, for being instrumental in destabilizing society and increasing radicalism. Engineers in the petrochemical industry have worked to cause climate change and pollution.


What I said re: Ukrainians also applies to Israelis... Israel would not exist if they weren't armed, because people - including Gazans - irrationally hate Jews and want them to cease to exist.

It's a good thing that Israel has the capability to defend itself. Which means killing a lot of Gazans.


I can’t tell if you are being sarcastic or not. But are you actually generalizing over an entire group of people who are currently undergoing a Genocide, and using that to justify their killings?


That's what it sounded like to me. I really hope I was missing some sarcasm.


It may have hurt me financially and limited my career opportunities, but this is one reason why I refuse to work on any technology that requires me to have a security clearance. It's a decision I made way back at the end of the last century and it has served me well throughout ~25 years of aircraft development while the world has been at continuous war, and mostly kept me out of military programs.

Also, I took one look at the SF86 and said F that, no government deserves that information, so I didn't get screwed in the Department of State OPM hack like all the other suckers.


> may have hurt me financially and limited my career

Weapons doesn’t pay as well as making people click ads. The people working on this stuff are usually doing so because they believe it’s the right thing.


Actually, working for DOD programs has several advantages:

1) The pay is pretty good. It's not FAANG-level pay, but it's generally better than non-FAANG pay, without so much competition.

2) The work-life balance is excellent, as long as it's in a place you want to live. No 80-hour weeks, as overtime is generally prohibited unless approved by the customer (and then you get overtime pay). Time is tracked and paid by the government on an hourly basis, so they don't allow overtime unless necessary. No unpaid "exempt" overtime.

3) Generally stable employment. It's hard to find people with a security clearance, so it's hard to get fired unless you're a really poor performer. You probably don't have to worry about dealing with stack ranking unlike many regular jobs.


It’s rather funny to me - that you cannot get security clearance unless you were born in the USA, against the backdrop of the level of contribution von Braun provided.


> you cannot get security clearance unless you were born in the USA

This is not true.


Is it only certain levels of security clearance then ?


Not that I know of. Even Yankee White and TS-SC can go to naturalised citizens. Hell, our current Secretaries of Energy and Homeland Security are foreign born.


Hope you find comfort in fact that smart guys in China don't have such reservations and smart guys in North Korea don't have any options.


> less interested in being part of the MIC than they used to be

It's just TC being too low

Plenty of us are happy, even pleased, to make weapons.


Rest assured, founders who'll lie to their applicant pool about that will lie to their applicant pool about anything inconvenient.


No. A lot of hypersonic stuff is partly classified. So the journalists are left with the definition: hypersonic speed is Mach 5 and higher. Mach 5 is where the heat produced in the boundary layer (by compression, mainly) is high enough that chemical reactions take place and you need to account for them in your computational fluid dynamics.

As a rule of thumb, when you hear boost-glide vehicle, the speed is close to Mach 20. If it’s air breathing (ramjet or scramjet) the speed is slightly higher than Mach 5, but probably less than Mach 10.


Are they targeting Mach 5? The second paragraph of TFA says "The company's long-term ambition is to develop a commercial aircraft that can travel at Mach 9".

They mention that goal a couple of places, and state that hypersonic is defined as Mach 5 or more.


Agreed, this has nothing to do with passenger flight, and the pretense is gross.

Thin vernier -> thin veneer btw


A fair bit of vehicles go well north of 5 already so propulsion aside I don’t think the hurdles are massive. And propulsion seems to be what everyone is focused on


You could make the same argument for a lot of software tech startups.

If you develop state-of-the-art data infrastructure software, novel data processing capabilities, or some other advanced software tech, it is routine to have an org under the US DoD as one of the earliest pilot customers. It is an open secret but many startups pretend like this isn't a standard part of that kind of business. The US DoD is a sophisticated early adopter of a lot of tech at a stage before most commercial enterprises are willing to engage.

The average person on the street may be a bit naive about this but the majority of deep tech startups are de facto "dual use" and none of this should be a surprise to someone that works in deep tech.


> All of these hypersonics companies are targeting mach 5 for a reason, which is that the material science hasnt caught up yet.

My understanding is that mach ~5 is when ramjets hit their limit and you have to transition to scramjets if you want to go faster.


That's also right around where aerodynamic forces are juuuuuuust starting to transition to disassociation and ionization in high flow areas, as the electrons are ripped from molecules in the air. Probably not a coincidence, because a very ooooof zone will be the ramjet intake, since ramjets need to slow the air to subsonic for combustion. Lots of these high mach ramjets have amazing cooling devices on the intake.

These RDEs are especially neat because the exhaust mass is moving supersonically but they're very choosy about the mix in the combustion chamber, so and air-breathing RDE will be doing some sort of voodoo in that department. If they riddle it out they might get a single engine that functions throughout the airspeed regime.


I appreciate the sentiment, but it sounds a bit like the case of I.T. vis-à-vis the NSA. As James Bamford said, one expects+assumes that the NSA is way ahead of the state of the civilian art. They have the budget.

Likewise this case. As an OTL civvie I'd expect that this tech under discussion lags whatever .mil is up to. Out to launch!


Maybe they can catch up and end up with a more cost-effective rocket, like SpaceX. But probably not.


> mach 5 for a reason, which is that the material science hasnt caught up yet

The X-15 did Mach 6 in the 60s. What materials and components are you referring to as cliffing us at Mach 5? Isn’t the simpler explanation that hypersonic flight is defined at Mach 5?


The X-15's had to be repainted after every flight, because the ablative coating was designed to wear off at speed. That's a huge expense, in both time and money. Worth it for a research craft, not worth it for any practical use.

In terms of materials, most of the newmake ultra fast aircraft are using inconel, which is more viable than it was back in the day. Some are using ceramic coatings of various sorts in hopes that they'll be able to develop something strong enough to be reused.

And that's not to say that they won't be able to come up with something, just that nobody has done it yet, or, has done it and has talked about it.


I’m not saying we don’t have work to do on materials. I’m narrowly pushing back on the assertion that these materials cause the Mach 5 threshold.


It does feel disingenuous, but its also nothing new. Military research has always been the one of the primary driving forces behind critical technology.

Commercial tech is vulnerable to all sorts of disruptions, regulations, and setbacks. If you make something that will make killing a whole bunch of people easier, rest assured theres a global market for it.


Weird that the term "drone" is used for what is plainly a missile.


No, it's weird that people think that only those dumb looking quadrotor helicopters are "drones", when "drone" was originally a term used for an unmanned missile or aircraft decoy. This usage dates back to 1936 or earlier.


That R/C planes, helicopters, and toys need bureaucratic government licensure is only explainable as outgrowth of "helicopter" (pun intended), fear-based parenting and the elimination of everything fun that might have the slightest potential risk and the acquiescence to intrusive control.


Some of the first non-apian drones to ever fly were "missiles".

You're going to have to invent time travel, go back over a century, and murder all of the people who started calling drones "drones" if you want to win this battle.


A crushed bit of paper could be a "missile."

The mass media put its thumb on the scale, lambasting phenomena by reforging certain words to create a culture of fear and taboo using such example words as "hacker", "terrorist", and "drone".

And while a Unabomber approach to language use is unlikely to influence anyone, it's important to know the history of multiple meaning of words because those are additional meanings because a single word means different things to different people based on situational factors. To suggest one meaning is more "right" than another is to champion some people's experiences and invalid others'.


>A crushed bit of paper could be a "missile."

As anyone who's played D&D knows, an arrow shot from a bow, or a rock shot from a slingshot, is a "missile".


Every vehicle is a drone as every algorithm is AI now. Marketing keeps the world rolling.


Cruise missiles that have wings and follow flight plans rather than ballistic trajectories are pretty much just drones and always have been.


> every algorithm is AI now

Dammit, I'm still working with computer "programs", you crazy kids!


Another comment points out the inevitability of this technology appearing in weapons long before any sort of passenger aircraft. So the likely marketing reason is a bit of gaslighting to avoid "issues" with some investors.


No warhead and it's meant to be reusable. Very different engineering for an actual missile weapon that is intended to fly once.


In certain scenarios it makes sense and is very effective to turn off GC in Java, because then most allocations would be just a bump. It is much easier to turn it off than have a system without it and turn it on.


Speaking of detonations, NASA is till interested in nuclear propulsion to reach Mars. This is reminiscent of projects Nerva and Orion/: https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...




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